In addition to propulsion for moving the aircraft forward, aircraft engines, either civil aircraft engines or military aircraft engines, also generate power for supplying attachments or auxiliaries of the gas turbine or for supplying aircraft-related systems such as the air conditioning system, for example. For generating power for supplying the attachments or auxiliaries and the aircraft-related systems it is known from the related art to draw mechanical power from a core engine of the gas turbine which is used, for example, to drive pumps and generators. DE 41 31 713 C2 describes an aircraft engine, for example, in which shaft power is drawn from a core engine and this shaft power is supplied to auxiliaries.
In aircraft development, a definite trend can be observed to the effect that increasingly more electrical power is required in the aircraft. The reason for this is that hydraulically and pneumatically operated devices or power units in the aircraft are replaced by electrically operated devices and that more and more power is needed per aircraft seat. Therefore, the aircraft engines must provide more and more electrical power.
For generating electrical power it is known from the related art to couple the shaft of the core engine of a gas turbine to a generator so that the mechanical shaft power drawn at the shaft may be converted into electrical power. However, this type of supply or generation of electrical power has the disadvantage that a displacement of the operating characteristic curve of the gas turbine in the characteristics map of the high-pressure compressor toward the surge limit can be noted. The surge limit in the characteristics map of the high-pressure compressor delimits the stable operating range of the gas turbine from the unstable operating range of the gas turbine. In order to ensure stable operation over the entire operating range and thus the load range of the gas turbine, a certain surge limit margin must be maintained. The effect that a displacement of the operating characteristic curve toward the surge limit can be observed increases with decreasing performance of the gas turbine, i.e., instabilities may occur in the lower load range of the gas turbine, i.e., during partial load operation.
In order to ensure reliable operation of the gas turbine even in its partial load range under the above-mentioned aspects, the approach of the related art is to design the gas turbine, its core engine in particular, to have a greater surge limit margin. This results in a greater overall length of the high-pressure compressor of the core engine in particular, as well as in a greater number of stages, a greater number of blades, and thus in greater weight and higher costs overall. If, however, the high-pressure compressor of the core engine is not designed to have a greater surge limit margin, then, according to the related art, the only alternative remains to lower the operating characteristic curve of the gas turbine, the core engine in particular, to the extent that a sufficient surge limit margin is maintained even during partial load operation. However, this has the effect that during full load operation the efficiency optima can no longer be achieved, resulting in lower efficiency.